The present invention relates to an improved method and apparatus for the laying of pipelines from marine vessels. The invention is particularly applicable to rigid pipelines.
The invention relates particularly to a pipelay system of the xe2x80x9cJ-Layxe2x80x9d type, in which lengths (or xe2x80x9cstalksxe2x80x9d) of pipe are raised to a substantial angle to the horizontal before being launched into the water from the vessel. Typically, the pipe is welded into double joint sections, typically 24 m in length at an onshore location before being loaded onto the vessel. As pipelaying progresses, the lowermost end of the raised stalk is connected to the uppermost end of the previously launched pipe, typically by welding, before being launched into the water. The uppermost end of the previously launched pipe must be clamped in position while the new stalk is connected to it, and a mechanism is required for controllably launching the new stalk, along with the existing pipe, once the connection is complete and the clamp is released. Examples of J-Lay systems are disclosed in U.S. Pat. No. 3,266,256, U.S. Pat. No. 3,585,806, U.S. Pat. No. 5,421,675 and U.S. Pat. No. 5,464,307.
The present invention is concerned with providing an improved J-Lay system.
In accordance with a first aspect of the invention there is provided marine pipelay apparatus for use on a vessel, comprising:
a pipe connecting station including means for connecting a lowermost end of a raised pipe stalk to an uppermost end of a previously launched pipeline;
pipe support means comprising a tower extending upwardly above said pipe connecting station for maintaining a raised pipe stalk at an angle determined by a required lay line with its lowermost end aligned with said pipe connecting station;
first, static clamp means for releasably securing an uppermost end of a previously launched pipeline in alignment with said pipe connecting station; and
pipe launching means for controllably launching said raised pipe stalk when said first clamp means is released; wherein:
said pipe launching means comprises second, mobile clamp means adapted to be releasably secured to the pipeline and elevator means whereby said second clamp means may be raised and lowered controllably over a predetermined stroke distance between a first, uppermost, zero stroke position and a second, lowermost, maximum stroke position, whereby the pipeline may be gripped alternately by said first and second clamp means, the pipeline being launched from the vessel in a stepwise manner by means of a repeating cycle comprising applying said first clamp means to the pipeline while the second clamp means is being raised towards its zero stroke position, transferring the load of the pipeline from the first clamp means to the second clamp means, and lowering the second clamp towards its maximum stroke position; and wherein:
said pipe connecting station, said tower and said pipe launching means are mounted on a main supporting structure adapted to be mounted at a main deck level of a vessel for fore/aft movement relative thereto and said static clamp means is mounted on a hang-off structure adapted to be mounted at said main deck level of said vessel for fore/aft movement relative thereto independently of said fore/aft movement of said main supporting structure.
Preferably, said mobile clamp means and said tower are pivotally mounted on said main supporting structure and said static clamp means is pivotally mounted on said hang-off structure.
Preferably also, said tower is mounted for pivotable movement about a first horizontal, port/starboard axis whereby said predetermined angle may be adjusted within a predetermined range, said mobile clamp means being mounted for pivotable movement about said first axis for alignment with said lay line, and said static clamp means is mounted for pivotable movement about a second horizontal, port/starboard axis parallel to said first axis.
Preferably, the static clamp means is located beneath said pipe connecting station and said mobile clamp means is located above the static clamp, the uppermost position of the mobile clamp being above the level of the pipe connecting station and the lowermost position of the mobile clamp being below the level of the pipe connecting station.
Preferably, said main supporting structure comprises a first support structure adapted to be mounted at said main deck level of said vessel, and a second support structure mounted on top of said first support structure, said tower, said pipe connecting station and said pipe launching means being mounted on said second support structure.
Preferably, said mobile clamp means includes a pipe clamping device mounted on a supporting beam structure and said elevator means comprises a plurality of hydraulic jacks connected to said supporting beam structure and operable to raise and lower said supporting beam structure relative to said static clamp means.
Preferably, said static and mobile clamp means are adapted to be split along respective transverse axes and retracted clear of said lay line.
Preferably also, said static and mobile clamp means are adapted to be partially retracted so as to provide a predetermined, limited clearance around said lay line.
Preferably, said tower means is adapted to support a first pipe stalk in a stand-by position extending substantially parallel to said lay line.
Preferably also, the apparatus further includes pipe-handling means adapted to raise a pipe stalk into said stand-by position and subsequently to shift said pipe stalk from said stand-by position into alignment with said lay line.
Preferably, the pipe handling means is adapted for raising a pipe stalk onto said tower.
Preferably also, said pipe-handling means includes a horizontal, elongate platform adapted to be located so as to extend in the fore/aft direction between the stern of the vessel and said main supporting structure, said platform being adapted to support a pipe stalk prior to said pipe stalk being raised onto said tower, pipe storage bays extending in the fore/aft direction on either side of said platform, and pipe lifting means comprising a traversing beam extending in the fore/aft direction and mounted for transverse port/starboard movement above said platform and said storage bays, said traversing beam including pipe hoisting means adapted to lift pipe from both the port and starboard sides of said traversing beam between said pipe storage bays, said traversing beam and said platform.
Preferably also, said traversing beam includes pipe preparation means mounted thereon.
Preferably also, said pipe preparation means includes pipe bevelling machines mounted on said beam at either end thereof for forming welding bevels on either end of a pipe stalk supported on said traversing beam, said bevelling machines being adapted for fore/aft movement along the length of said traversing beam.
Preferably also, said platform includes a first pipe transporting trolley mounted for fore/aft movement along the length of said platform and including pipe clamping means for engaging and supporting a first end of a pipe stalk at a sternmost end thereof.
Preferably, said pipe clamping means is adapted for pivotable movement about a horizontal port/starboard axis.
Preferably also, said pipe-handling means includes a pipe-hoisting device which is adapted to be raised and lowered relative to said pipe supporting means, said device including:
pipe hoisting means;
a main body portion adapted for connection to said pipe hoisting means;
pipe clamping means connected to said main body portion and adapted to engage an outer surface of one end of a pipe stalk, said pipe clamping means being adapted for pivotable movement relative to said main body portion about a horizontal port/starboard axis;
a housing mounted on said main body portion and including winch means adapted for connection to an internal line up clamp (ILUC), such that said ILUC may be stored in said housing and deployed therefrom, through said clamping means and along the interior of a pipe stalk gripped by said clamping means.
Preferably also, said clamping means and housing are connected to said body portion by actuating means operable to effect movement of said clamping means and said housing relative to said body portion in a fore/aft direction between a first stand-by position and a second position in which said clamping means is aligned with said lay line.
In accordance with a second aspect of the invention, there is provided a marine pipelay vessel equipped pipelay apparatus in accordance with the first aspect of the invention.
Preferably, said lay-line extends through a moon-pool formed in the vessel.
In accordance with a third aspect of the invention, there is provided a marine pipelay method for laying a pipeline from a vessel utilising apparatus in accordance with the first aspect of the invention, the method comprising the steps of:
(a) raising a first pipe stalk to a required launch angle;
(b) lowering said first pipe stalk along said lay line until its uppermost end is aligned with said pipe connecting station;
(c) clamping said uppermost end of said first pipe stalk using said static clamp means;
(d) raising a second pipe stalk to said required launch angle and connecting its lowermost end to the uppermost end of said first pipe stalk;
(e) securing said mobile clamp means to said first pipe stalk at said first, uppermost position, releasing said static clamp means and operating said mobile clamp means to lower the first and second pipe stalks until the mobile clamp means reaches said second, lowermost position, and repeating the foregoing steps, if required, until the upper end of the second pipe stalk is aligned with the pipe connecting station;
(f) securing said static clamp means to the uppermost end of said second pipe stalk;
(g) releasing said mobile clamp means and returning said mobile clamp means to said first position;
(h) repeating steps (d) to (g) until the required length of pipeline has been laid.
Preferably, the steps of raising said pipe stalks include preliminary steps of raising said pipe stalks into a stand-by position in which the pipe stalk extends along an axis substantially parallel to but spaced from said lay line, and subsequently shifting the pipe stalk from said stand-by position into alignment with said lay line.
Preferably, the method includes an initial step of lifting the pipe stalks from a storage area onto a preparation platform and bevelling the ends of the pipe stalk prior to raising the pipe stalk to said required launch angle.
Preferably, a pipe stalk being lowered includes a projection greater than the outer diameter of the pipe and less than a predetermined diameter, wherein step (e) of the method defined above includes the following steps whereby said projection may be passed through said static clamp means when said static clamp means is released and said mobile clamp means is operated to lower the pipe stalk:
prior to the projection reaching the static clamp means, with the load of the pipe supported by the static clamp means, opening a first pipe guide located on top of the static clamp means to a retracted position providing sufficient clearance to pass said projection;
transferring the load of the pipe from the static clamp means to the mobile clamp means by engaging the mobile clamp means and releasing the static clamp means;
opening the static clamp means to a retracted position providing sufficient clearance to pass said projection;
operating said mobile clamp means to lower the projection to a position below said first pipe guide and within said static clamp means;
closing said first pipe guide;
opening a second pipe guide located beneath the static clamp means to a retracted position providing sufficient clearance to pass said projection;
operating said mobile clamp means to lower said projection to a position below said second pipe guide;
closing said second pipe guide, closing said first pipe guide and transferring the load of the pipe from the mobile clamp means to the static clamp means.
These and other aspects and preferred features of the invention will be described in the following description of embodiments of the invention.
Another known type of pipe-launching system in which the pipe is paid out in a step-wise manner using a first, static clamp and a second, travelling clamp is disclosed in EP-A-0522050 (Coflexip SA).